The tracking microscope will be used to characterize photoresponses due to rhodopsin in the bacterium Halobacterium halobium. Genetic techniques will be used to determine the sequence of steps leading from the excitation of rhodopsin to flagellar control. Mutants will be isolated and characterized which have altered rhodopsins, altered receptor membranes, or altered responses. Depending on the availability of mutants, biochemical studies will be initiated on the retinal-opsin interaction, the structural organization of the receptor membrane, and/or the mechanism of transfer of information from membrane to flagellae. The goal is an understanding of molecular processes relevant to vision.